Water-resistant microcapsular opacifier system and products

ABSTRACT

MICROCAPSULES HAVING CONTROLLED STRUCTURAL INTEGRITY ARE PRODUCED BY A PROCESS WHICH INVOLVES ADMIXING OIL-SOLUBLE, PARTIALLY-CONDENSED THERMOSSETING CONDENSATION POLYMERCONTAINING OILY SOLUTION AND A WATER-SOLUBLE POLYMER CONTAINING AQUEOUS SOLUTION AND CAUSING A CHEMICAL REACTION BETWEEEN THE POLYMERS AT THE RESULTING OIL/WATER INTERFACE. THE MICROCAPSULES ARE ACTIVATED BY EXPELLING THE OILY CORE MATERIAL AND REPLACING IT WITH AIR AND CURED TO PROVIDE OPACIFIERS HAVING EXCELLENT WATER RESISTANCE AND MAY BE EMPLOYED AS OPACIFYING AGENTS IN COATINGS AND PARTICULARLY IN PAINT FILMS.

I Patent [191 111 3,779,941

Powell 45 Dec. 18,1973

[54] WATER-RESISTANT MICROCAPSULAR 3,460,972 8/1969 Nack 252/316 XOPACIFIER SYSTEM AND PRODUCTS 3,585,149 6/1971 Vassiliades et al.252/316 75 I t M b' P.P ll,Ch' ,lll. nven or a rm owe [Cage PrimaryExaminer-Richard D. Lovering [73] Assignee: Champion InternationalAttorney-Roylance, Abrams, Berdo and Kaul Corporation, New York, NY.

[22] Filed: July 17, 1970 57 ABSTRACT [21] Appl' 55925 Microcapsuleshaving controlled structural integrity are produced by a process whichinvolves admixing oil- [52] US. Cl .1 252/316, 106/312, 117/100 A,Soluble, partially-Condensed thermosetting nden 117/161 C, 117/161 F,1-17/161 1,, {17/161 tion polymer-containing oily solution and a 'water-LN, 117/161 UC, 1 17/161 UZ 260/25 13 soluble polymer-containing aqueoussolution and caus- 260/2.5 F, 264/4 ing a chemical reaction between thepolymers at the re- [51] Km. C1. B01j 13/02, B44d 1 /02 C09d 5/00sulting oil/water interface. The microcapsules are acti- [58] Field ofSearch 252/316; 117/100 A; vated by expelling the oily core material andreplacing 264/4; 106/312; 260/25 F 25 B it with air and cured to provideopacifiers having excellent water resistance and may be employed asopacify- [56] Referen e Cited ing agents in coatings and particularly inpaint films.

UNITED STATES PATENTS 3,432,327 3/1969 Kan et al. 252/316 X 23 Claims, 2Drawing Figures OILY SOLUTION OF PARTIALLY CONDENSED FORMALDEHYDECONDENSATION PRODUCT AQUEOUS POLYMERIC SOLUTION EMULSIFICATION HEAT T0INDUCE INTERFACIAL REACTION] ACTIVATE PRECURSOR MICROCAPSULES TO FORMOPACIFYING AGENTS AND FURTHER PROMOTE CROSSLINKING BY SPRAY DRYINGDISPERSE MICROCAPSULAR DISPERSE PRECURSOR MICRO- OPACIFIERS IN AQUEOUSCAPSULES WITH CLAY AND PAINT SYSTEM OR SOLVENT BINDERS TO FORM ANAQUEOUS SYSTEM PAINT SYSTEM CAST PAINT FILM, ACTIVATE AND CURE PMFNIEIIIIEI? I 8 I975 SIIIET 1B? 2 OILY SOLUTION OF PARTIALLY CONDENSEDFORMALDEHYDE CONDENSATION PRODUCT EMULSIFICATION AQUEOUS POLYMERICSOLUTION HEAT TO INDUCE INTERFACIAL REACTION SPRAY DRYING ACTIVATEPRECURSOR MICROCAPSULES TO FORM OPACIFYING AGENTS AND FURTHER PROMOTECROSSLINKING BY DISPERSE MICROCAPSULAR OPACIFIERS IN AQUEOUS PAINTSYSTEM OR SOLVENT SYSTEM DISPERSE PRECURSOR MICRO- CAPSULES WITH CLAYAND BINDERS TO FORM AN AQUEOUS PAINT SYSTEM FIGI CAST PAINT FILM,ACTIVATE AND CURE INVENTOR MABRIN P. POWELL BYEQQ a M WIM ATTORNEYSmmnunm 1 8 I975 3,779,941

SHEET 2 CF 2 OILY SOLUTION OF PARTIALLY CONDENSED FORMALDEHYDECONDESATION PRODUCT AQUEOUS POLYMERIC SOLUTION EMULSIFICATION HEAT TOINDUCE INTERFACIAL REACTION MIX PRECURSOR MICROCAPSULES WITH BINDER TOFORM AQUEOUS PAINT SYSTEM ACTIVATE PRECURSOR CAPSULES IN SITU BY DRYINGPAINT FILM FIG.2

INVENTOR MABRIN F. POWELL BY 2 14,42 aka/M,

A 7' TORNE Y8 WATER-RESISTANT MICROCAPSULAR OPACIFIER SYSTEM ANDPRODUCTS This invention relates to the art of microencapsulation. Moreparticularly, this invention relates to the production ofwater-resistant microcapsules and to microcapsular opacifying systems.

Microcapsular products have been employed extensively in a wide range ofproducts, including pharmaceuticals, foods, cosmetics, adhesives,adhesive tapes, fertilizers, and the like. Additionally, microcapsuleshave been employed in the art of transfer-copy systems wherein minutedroplets of a colorless dye intermediate material are dispersed ordissolved in an oil, encapsulated, and thereafter coated onto a transfersheet. The transfer sheet is employed in combination with an underlyingcopy sheet having an absorbent coating thereon containing material whichcan react with the dye intermediate and form a visible colored mark. Thepressure from an ordinary stylus or typewriter causes the capsulesimmediately adjacent thereto to rupture and release the dye intermediatewhich reacts with the underlying copy sheet at points where themicrocapsules have been ruptured.

U.S. Pat. No. 3,418,250 and U.S. Pat. No. 3,418,656, to A. E.Vassiliades describe the production of microcapsules having walls formedof a thermosetting and/or a thermoplastic resinous material. Suchmicrocapsules are highly suitable for use in pressure-responsive,transfercopy systems, and the like. The process for formingmicrocapsules involved in such patents involves admixing awater-immiscible oily material and/or water-andoil-immiscible organicliquid solution of a thermoplastic resin with an aqueous medium therebycausing the resin to separate from solution in solid particle form abouta nucleus of oily material.

Prior microencapsulation processes have involved, for example, theformation of an oil-in-water emulsion followed by the addition of anaqueous solution of a wall-forming polymeric material. In addition, suchprocesses have utilized a crosslinking or curing agent that must beadded in order to harden the capsular walls of the microcapsules. Stillother encapsulation processes require the addition of acids in order toproduce condensation and/or cause precipitation of the polymericwall-forming material. 7

Likewise, microcapsules have been produced by a procedure involvinginterfacial polycondensation whereby two reactants are brought togetherat a reaction interface wherein polycondensation occurs to form acapsule shell consisting of a high molecular weight condensationpolymer. This technique is described, for example, in U.S. Pat.3,429,827 to Ruus. Another microencapsulation technique involving theaddition polymerization of monomers is described in U.S. Pat. No.2,969,330 to Brynko. Still another process for encapsulation describedin U.S. Pat No. 3,432,327 to Kan et al. which describes the preparationof a pressure sensitive copying sheet coated with microcapsules formedby the interfacial reaction of polymeric substances at the interface ofhydrophobic and hydrophilic liquids.

It has been proposed to employ air-containing microcapsules having anaverage particle size below about one micron as opacifying agents incoatings, on fibrous substrates, and in non-fibrous substrates. Thesemicrocapsular opacifying agents possess an opacifying power equal to orsubstantially greater than any known inorganic pigment on a weightbasis. The incorporation of microcapsular opacifiers into surfacefinishes, such as paints, requires that the opacifiers have additionalproperties including scrubability, freeze-thaw stability, and the like.Thus, the microcapsular opacifiers employed in surface coatings shoulddesirably possess a high resistance to water in order that the paintedsurface withstand repeated washings, for example.

It has now been found that microcapsular opacifiers may be producedhaving excellent water-resistance, controlled wall strength, uniformityof particle size and which yield surface finishes having excellenthiding power when employed in surface coatings, such as paint films andthe like. According to the present invention, a process is provided forthe formulation of microcapsular precursor opacifiers which comprisesadmixing:

a. a solution comprising an oil-soluble, partially condensedthermosetting condensation product in a water-immiscible oily material;and

b. an aqueous solution of a water-soluble polymeric material;

thereby forming an emulsion, said thermosetting condensation product andsaid water-soluble polymeric material being capable of interaction toform a solid resinous material, and subjecting said emulsion toconditions whereby said polymeric materials react to form microcapsuleshaving solid capsular walls about a nucleus of said oily material. Theprecursor capsules are then treated to expel the oily core material andreplace it with air.

Surprisingly, it has been discovered that by providing an oil-soluble,thermosetting condensation product as a wall-forming material in an oilphase and admixing this oily solution with a water-soluble polymer in anaqueous phase, microcapsular opacifiers are produced having unexpectedlygood water resistance. The employment of a thermosetting condensationproduct that is soluble in oil rather than in water permits thethermosetting condensate to concentrate mainly in the oil phase of theemulsion droplet by virtue of its greater lypophilic characteristics.This results in a more efiicient utilization of the thermosettingcondensation product in the capsule wall, since lesser amounts of suchresinous materials need be employed as compared with systems utilizingwater-soluble thermosetting condensates.

The oil-soluble, partially condensed, thermosetting condensationproducts of the present invention includes A-stage or B-stage resins,i.e., resins not having reached the infusible or insoluble stage.However, the B-stage resins are especially preferred for the purposes ofthe present invention.

Exemplary of suitable oil-soluble resins are the condensation reactionproducts of formaldehyde with phenols, such as, hydroxybenzene (phenol),m-cresol and 3,5-xylenol; carbamides, such as urea; triazines, such asmelamine; amino and amido compounds, such as, aniline,p-toluenesulfonamide, ethyleneurea and guanidine; and the like. Underthe influence of heat, these resins change irreversibly from a fusibleand/or soluble material into an infusible and insoluble material.

The preferred formaldehyde condensation products employed in thisinvention are partially-condensed melamine-formaldehyde,phenol-formaldehyde and urea-formaldehyde resins. The B-stage melamineand urea-formaldehyde resins are especially preferred.

Oil-soluble partially condensed resins may be easily prepared accordingto conventional practices. For example, partially condensedthermosetting resins may be made compatible with various oily solventsby alkylating the resin with an alkanol, such as butanol or acombination of butanol with a higher alkanol, such as octyl alcohol orthe like. For example, the preparation of a suitable oil-solublemelamine-formaldehyde and its modification with butanol is described onpages 460461 of Preparative Methods of Polymer Chemistry, by Wayne R.Sorenson (InterScience Publishers, 1961), the disclosure of which ishereby incorporated by reference.

The substitution of a portion of the butanol alkylating agent by thehigher alkanol increases the compatibility of the resin, e.g., melamineformaldehyde, with the hydrocarbon solvent. The properties of suchmelamine resins are described on pages 192 and 193 of Amino Resins byJohn F. Blais (Reinhold Publishing Corp., N.Y., 1959).

Any suitable oily material may be employed in the preparation of theoily solution of the partially condensed formaldehyde condensationpolymer of the present invention. As previously mentioned, the oilymaterial in the precursor microcapsules is driven from the microcapsulesand is replaced by air. The oily material of the present inventionincludes lipophilic materials which are preferably liquid, such as oils,which will not mix with water and which can be driven through theporous, solid walls of the present precursor microcapsules. The oilymaterial may be a low melting fat or wax. However, oils are thepreferred oily material, since they do not require special temperaturemaintenance during the production of the microcapsules. Furthermore,oils are more easily volatilized and driven through the micropores ofthe walls of the microcapsules.

In general, the lipophilic nucleus materials may be natural or syntheticoils, fats, and waxes or any combination thereof which can be removedfrom the microcapsules at the desired temperatures. Among the materialsthat can be employed in the process of the present invention are:aliphatic hydrocarbons, for example, heptane, octane, decane or mixturesof such materials, for example, mineral spirit products and the like.

The preferred oily materials for employment in the present invention arethose oils having a fairly high vapor pressure (high volatility), sothat they can be completely and easily expelled through the microporesof the solid-walled microcapsules over a wide range of temperatures,e.g., by the application of moderate amounts of heat, e.g., -32 to180C., preferably between about to about 100C. It is especiallypreferred to employ oils which can be driven from the microcapsules attemperatures conventionally employed in the drying of paper webs orpaper coatings, e.g., about 85C. Preferred oils for use in the presentinvention include mineral spirits, benzene, xylene, toluene, styrenemonomer, turpentine, and oils having a like volatility. 1 Y

The water-soluble polymeric material of the present invention functionsas an emulsifying agent in addition to its being a wall-former. Thewater-soluble polymeric material of the present invention reactschemically with the partially condensed formaldehyde condensationproduct dissolved in the oil phase'at the oil-water interface to form asolid microcapsular shell. Suitable watersoluble polymers which may beemployed in the present invention include thermoplastic resins,- such aspolyvinyl alcohol, methyl cellulose, a styrene-maleic acid salt, e.g.,the sodium or ammonium salt thereof, the the like. The preferredwater-soluble polymer is a styrene-maleic acid ammonium salt. However,any water-soluble polymer that is capable of reacting with theformaldehyde condensation polymer at the oil-water interface to form asolid shell may be utilized.

An oil-in-water emulsion is formed by admixing the oily solution of theformaldehyde condensation product and the aqueous polymeric solutionunder conditions of brisk agitation. Brisk agitation is employed inorder to obtain very small droplets of the emulsion, and, ultimately,very small capsules. Thus, microcapsules having diameters ranging fromabout 0.1 to several hundred microns can be produced depending upon thedegree of agitation. In order to produce suitable opacifying agents, themicrocapsules produced by the process of the present invention must havean average particle size of below about 1 micron, and preferably betweenabout 0.25 and about 0.8 micron. Agitation may be achieved by means of ahigh speed mixer or impeller, by ultrasonic waves or by otherconventional means.

If desired, a relatively small amount, e.g., between about 0.5 and about5 percent, preferably between about 2 and about 3 percent by weight ofthe oily solution of a natural or synthetic wax may be added to the oilysolution of the thermosetting condensation product to further increasethe water resistance of the capsular walls. Thus, a wax modifying agent,such as candelillia wax, caranauba wax, low molecular weight syntheticwaxes, such as polyethylene and paraffin waxes may be added to the oilypolymeric solution which, in combination with formaldehyde condensateremaining inside the microcapsule after the core solvent has beenexpelled through the permeable walls of the microcapsules, furtherincreases the water resistance of the microcapsular walls.

After the formation of the oil-containing microcapsules, these opacifierprecursors are treated to remove the oily core material and replace thesame with air. Thus, for example, the precursor microcapsules may beheated to temperatures which cause the oily core material to volatilizeand pass through the micropores in the solid walls of the capsules. Inthe case of microcapsular opacifiers to be used on fibrous substrates,the oily material may be driven from the microcapsules either before orsubsequent to their being coated onto the substrate. For example, adispersion of the oil-containing microcapsules may be spray-dried so asto provide aircontaining microcapsules, which may be then coated ontothe substrate.

The microcapsular opacifiers of the present inventionare particularlyuseful in surface coatings where resistance to water is required. Thus,the instant opacifiers find particular application in paintformulations. The microcapsular opacifiers may be mixed with inorganicpigments and additional binders, such as a latex binder to form anaqueous paint system. Likewise, the opacifiers may be suspended in asolvent to produce a solvent-based paint system. These paintformulations possess a substantially greater hiding power than paintfilms of the same thickness which contain inorganic pigments, such astitanium dioxide as the opacifying agent. In addition, paintformulations containing the microcapsular opacifiers of the presentinvention possess scrubability, freeze-thaw stability and otherproperties equal to paint formulations containing commonly used titaniumdioxide pigments.

Referring now to the drawings, alternative modes of providing paintsystems containing the air-containing microcapsular opacifiers of thepresent invention are illustrated.

In the encapsulation process shown in FIG. 1, an oily solution of apartially condensed formaldehyde condensation product, e.g.,melamine-formaldehyde is admixed with an aqueous solution of a polymericmaterial, e.g., methyl cellulose, and emulsification is continued underconditions of brisk agitation until the desired particle size isobtained, e.g., below one micron. Emulsification is conducted, forexample, at a temperature in the range of between about 25 and about95C., preferably between about 30 and about 40C.

Next, the emulsion is heated to a temperature sufficient to cause theoil-soluble polymer and the watersoluble polymer to react at theoil-water interface. Suitable temperatures to cause such interactionare, for example, between about 50C. and about 95C., preferably about50C. to 60C., depending upon the particular system involved.

According to one embodiment illustrated in FIG. 1, the microcapsules arethen activated, i.e., the oily core material is driven off at this pointin the system. This may be accomplished by spray-drying the precursorcapsules, subjecting the capsules to a vacuum, or otherwise treating thecapsules to drive the oily material from the interior of themicrocapsules and replace it with air. It is especially preferred tospray-dry the capsules, thereby driving the oily material from thecapsular core while promoting crosslinking of the capsule walls. Oncethe oily core has been replaced with air, the capsules may be fullycured. Suitable activation temperatures include between about ambienttemperature and 180C, preferably between about 80C. and about 90C., forexample.

The resultant opacifiers may be either dispersed in an aqueous paintsystem, or may be dispersed in a solvent and formed into a solvent basedpaint.

According to another embodiment, the precursor microcapsules may bedispersed with clay and binders to form an aqueous paint system which isthen cast into paint film which is thereafter cured by heating, e.g., at180C. for seconds, or by curing the paint system for 30 days at ambienttemperature, for example.

In the embodiment shown in FIG. 2, the oilcontaining microcapsularprecursors are not activated immediately after their formation, as inthe method of FIG. 1. Rather, the precursor microcapsules are mixed withbinders, such as clay and latex, to form an aqueous paint system. Next,the paint formulation is applied to the desired substrate to formaqueous paint film, and the paint film is dried at ambient or elevatedtemperatures to activate the precursor microcapsules and permit the oilycore material to escape. In this manner, the opacifiers are produced insitu without the need for an additional activation step.

EXAMPLE 1 Twenty grams of a 50 percent by weight of a melamineformaldehyde solution in a xylol-butanol mixture is diluted with gramsof mineral spirits to a total weight of grams of solution. The melamineformaldehyde solution is emulsified with grams of a 5 percent by weightaqueous solution of a copolymer of styrene-maleic acid (ammonium salt).Emulsification is continued until particles of the desired size anduniformity, viz., below about one micron, are obtained.

Next, the emulsion is heated to a temperature of 50C. while underagitation for approximately 6 hours to induce an interfacial reactionbetween the partially condensed formaldehyde condensation polymer andthe styrene-maleic acid copolymer at the water/oil interface therebyforming microcapsules. A partial curing of the capsules is effectedduring the heating period. The extent ,of, curingmay be varied depending7 upon desired properties of the final product and its application.

EXAMPLE 2 The microcapsular dispersion produced in Example 1 isactivated to remove the oily core by injecting the dispersion by meansof a fine air feed nozzle into a spray drying chamber heated to atemperature of about 100C. Optionally, the activated microcapsules maybe subjected to a subsequent drying treatment in a fluidized bed inorder to provide additional crosslinking of the wall materials. Thedried air-containing microcapsular product is collected, mixed withinorganic pigments, and the mixture is dispersed in an aqueous paintsystem.

The paint is applied to a substrate and the resulting paint film hasexcellent hiding power and resistance to water.

EXAMPLE 3 An aqueous solution of 7 percent by weight styrenemaleic acidammonium salt is prepared having a pH of 7.0 at 25C. Meanwhile, a 20percent by weight solution of a melamine-formaldehyde (50 percent byweight in xylene-butanol) in mineral spirits is prepared by simpledilution of the melamine-formaldehyde with the mineral spirits.

An oil-in-water emulsion is prepared in a high-shear mixer, by admixing100 grams of the melamineforrnaldehyde in mineral spirits solution with150 grams of the aqueous styrene-maleic acid copolymer solution at atemperature of 25C.

Next, 10 milliliters of a 5 percent by weight solution of sulfamic acidis added to the emulsion and dispersed well therein. The emulsion isthen heated at a temperature of 40C. for a period of two hours tochemically react the styrene-maleic acid with the melamineformaldehydeand form precursor microcapsules containing oil.

EXAMPLE 4 Clay and a latex binder are added to the microcapsulardispersion of Example 3 to form an aqueous paint formulation. Next, theresulting paint system is coated onto a substrate and the paint film isdried at a temperature of about 100C. in order to drive the oily corematerial from the precursor capsules present in the paint film. Theresulting paint film has excellent water resistance.

EXAMPLE 5 The procedure of Example 4 is repeated with the exception thatthe paint film is permitted to dry at ambient temperature for thirtydays.

As in the case of the prior example, the film has good resistance towater.

This invention has been described in detail with particular reference tothe preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention as described hereinabove and as defined in the appendedclaims.

What is claimed is:

l. A method for the formation of microcapsular opacifying agents whichcomprises admixing a. an oily solution comprising an oil-soluble,partially-condensed' thermosetting condensation product in awater-immiscible oily material; and

b. an aqueous solution of a water-soluble polymeric 'material; therebyforming an emulsion, said thermosetting condensation product and saidwatersoluble polymeric material being capable of interacting to form asolid, resinous material, subjecting said emulsion to conditions wherebysaid polymeric materials react to form precursor microcapsules havingsolid capsular walls about a nucleus of said oily material, andactivating said microcapsules to provide microcapsular opacifying agentsby expelling said oily core material and replacing said oily corematerial with air.

2. The method of claim 1 wherein said microcapsules are activated byheating at a temperature in the range of between about ambienttemperature and about 180C.

3. The method of claim 1 wherein said precursor microcapsules have anaverage particle diameter below about 1 micron.

4. The method of claim 3 therein said precursor microcapsules have anaverage particle diameter between about 0.25 and about 0.8 micron.

5. The method of claim 1 wherein said oil-soluble, partially condensedthermosetting condensation product is a formaldehyde condensationproduct.

6. The method of claim 5 wherein said formaldehyde condensation productis an oil soluble melamineformaldehyde, urea-formaldehyde orphenolformaldehyde.

7. The method of claim 6 wherein said formaldehyde condensation productis an oil soluble melamineformaldehyde.

8. The method of claim 7 wherein said oil-soluble melamine-formaldehydeis a butylated melamineformaldehyde.

9. The method of claim 1 wherein said water-soluble polymeric materialis a salt of a styrene-maleic acid copolymer, methyl cellulose orpolyvinyl alcohol.

10. The method of claim 9 wherein said watersoluble polymeric materialis polyvinyl alcohol.

11. The method of claim 9 wherein said watersoluble polymeric materialis a styrene-maleic acid ammonium salt.

12. The method of claim 1 wherein said oily solution additionallycontains a wax modifying agent.

13. A method for the formation of microcapsules which comprises admixinga. an oily solution comprising an oil-soluble, partially-condensedthermosetting condensation product in a water-immiscible oily material;and

b. an aqueous solution of a water-soluble polymeric material; therebyforming an emulsion, said thermosetting condensation product and saidwatersoluble polymeric material being capable ofinteracting the form asolid product, subjecting said emulsion to condition whereby saidpolymeric materials react to form microcapsules having solid capsularwalls about a nucleus of said oily material.

14. The method of claim 13 wherein said emulsion is heated at atemperature in the range of between about 50 and about C. to formmicrocapsules.

15. The method of claim 14 wherein said thermosetting condensationproduct is a formaldehyde condensation product.

16. The method of claim 15 wherein said formaldehyde condensationproduct is an oil soluble melamineformaldehyde, urea-formaldehyde, orphenolformaldehyde.

17. The method of claim 16 wherein said formaldehyde condensationproduct is an oil soluble melamineformaldehyde.

18. The method of claim 17 wherein said watersoluble polymeric materialis a styrene-maleic acid copolymer, polyvinyl alcohol, or methylcellulose.

19. The method of claim 17 wherein said watersoluble polymeric materialis polyvinyl alcohol.

20. The method of claim 19 wherein said oil-solublemelamine-formaldehyde is a butylated melamineformaldehyde.

21. The method of claim 13 wherein said oily solution additionallycontains a wax modifying agent.

22. An opacifying agent as produced by the method of claim 1.

23. A precursor microcapsule produced by the method of claim 13.

UNITED STATES PATENT OFFICE Q ER'ljl'FlCAT-E 0F CORRECTEQN PatentNo.3,779, ?!+l Dated December 18,1973

Inventor(s) Mabrin P We1l It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 8, line 21, "condition should read --conditions.

Signer. and sealed this 16th day of April 191 2 (SEAL) Attest: I

EDI -IARD M .FLETCHER, JR C I IJ XRSHALL DANN Attesting, OfficerCommissioner of Patents Pf pscoMM-oc wan-Poo 4 4 1 f 11.5. mun m'mfmdomen no o-su-su.

UNITED STATES PATENT OFFICE QER'llFICAT-E ()F CORRECTION PatentNo.3,779, Dated ecember 18,1973

Inventofls) Powell It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 8, line 21, "condition should read --conditions-.

Signer and this 16th day of April 19714..

(SEAL) Attest:

EDWARD M.FLET 0HER;JR. I c MARSHALL DANN AttestingOfficer v Commissionerof Patents fQ-WSBQO- pscoMM-Dc wan-Pen

